I use a few weird tricks here. Functions that transition to kernel mode via syscall are all X64-style "fastcall", and if they fault, no big deal. So I call them all with invalid parameters because even if the function fails, I'm still getting the syscall index.

I haven't and probably won't provide a method of getting X86 syscalls, but considering there likely won't be any new X86 operating systems (syscall indices for WOW64 syscalls is same as X64) you can safely use already documented syscall indices (or rewrite this slightly)